1. Field of the Invention
The present invention relates to a secondary battery pack in embodiments thereof.
2. Description of the Related Art
Among rechargeable secondary batteries, a lithium secondary battery which is most greatly attracting public attention as a next-generation power source has high energy density without a memory effect, and when not in use, the chance of internal current leakage is low, and is very lightweight. Therefore, the lithium secondary battery is widely used in various portable electronic devices such as a notebook computer, a camera, or a mobile phone, as well as, due to characteristics of high energy density, frequency in use thereof tends to be gradually increased in fields such as defense industries, automated systems, automobiles, and aerospace industries. In particular, the lithium secondary battery is widely commercially used as a motor driving source of an electric vehicle and a hybrid vehicle.
Such a lithium secondary battery may be generally classified into a lithium ion battery using a liquid electrolyte and a lithium polymer battery using a polymer electrolyte depending on a type of electrolytic solutions. In addition, such a secondary battery is manufactured in various shapes, and may be classified into cylindrical, prismatic, and pouch shapes depending on a shape thereof.
Further, the lithium secondary battery typically includes: an electrode assembly including a cathode plate in which a cathode active material is coated on a collector, an anode plate in which an anode active material is coated on the collector, and a separation membrane which is disposed between the cathode plate and the anode plate, so as to allow only lithium ions to move therethrough while preventing a short-circuit therebetween; a case which houses the electrode assembly; a electrolytic solution which is contained inside of the case to allow the lithium ions to move; and the like.
In particular, the pouch type lithium secondary battery is significantly lighter than an aluminum case, and has a case made of a pouch packaging material, such that it is possible to have a higher energy density than the prismatic lithium secondary battery.
In such a secondary battery, since a single battery has a low power and a small capacity, when applying to equipment such as an electric vehicle or hybrid vehicle which requires a longer term driving capability and high electrical power, it has been used in a form of a secondary battery module and secondary battery pack in which a plurality of secondary batteries are laminated in the case, and electrically connected with each other, and sensing lines for sensing a voltage and temperature, etc. are included therein.
However, in the secondary battery, a decrease in performance is small even when repeatedly charging and discharging, whereas even if being exposed to abnormal usage environments such as overcharge, short-circuit, reverse connection, or heat exposure, gas is generated due to an electrochemical action in the battery, to increase a battery internal pressure, and thereby the battery may be expanded. Further, if an abnormal operation such as an overcharge is continued for a long time, the electrolyte or the active materials in the battery are decomposed, and the internal pressure and the temperature are rapidly increased, which may result in an explosion or fire of the battery.
Accordingly, a secondary battery pack, in which one or more of unit cells capable of including the secondary battery or a secondary battery module are combined with each other, needs to include: end plates for combining the unit cells without allowing damage due to a pressure generated by the expansion of the battery; a connecting bar for connecting the end plates with each other; and a safety device capable of stopping an operation of the battery pack such as charging of the battery, when the expansion generated in the battery reaches a predetermined value. In addition, as the secondary battery pack is often used in a restricted space, it is necessary to minimize an increase in a size or length while satisfying the above-described requirements.
There are many techniques relating to the secondary battery disclosed in the patent documents such as European Patent Registration No. 0613201 (1998 Aug. 12), U.S. Pat. No. 6,218,039 (2001 Apr. 17), U.S. Pat. No. 7,125,628 (2006 Oct. 24), and U.S. Pat. No. 8,846,238 (2014 Sep. 30), U.S. Patent Application Publication Nos. 2011/0262785 (2011 Oct. 27), 2012/0189879 (2012 Jul. 26), 2014/0239904 (2014 Aug. 28), 2011/0177377 (2011 Jul. 6), and 2011/0200862 (2011 Aug. 18), Korean Patent Laid-Open Publication Nos. 10-2007-0101025 (2007 Oct. 16), 10-2011-0075369 (2011 Jul. 6), 10-2011-0117586 (2011 Oct. 27), and 10-2012-0048280 (2012 May 15), and Korean Patent Registration No. 10-1255250 (2013 Apr. 10).